Preoperative or postoperative start of prophylaxis for venous thromboembolism with low-molecular-weight heparin in elective hip surgery?

BACKGROUND: Prophylaxis of venous thromboembolism with low-molecular-weight heparins in patients undergoing major orthopedic surgery is currently initiated according to at least 3 different regimens. In Europe, traditionally, prophylaxis is started 12 hours before surgery, whereas in North America it is initiated 12 to 48 hours postoperatively. The third regimen (perioperative) begins prophylaxis either earlier than 12 hours before or 12 hours after surgery. Unfortunately, the optimal regimen is uncertain because direct comparisons among these regimens with sufficiently large sample sizes are not available.
OBJECTIVE: To assess, in a systematic review, the relative efficacy and safety of the 3 low-molecular-weight heparin regimens used to prevent thrombosis after total hip replacement. The incidence of postoperative thrombosis detected by contrast venography was used as the measure of efficacy and the rate of major bleeding was used as the measure of safety.
METHODS: We pooled the results of all published studies, which met the following criteria: (1) inclusion of in at least 1 arm of the study of a dose of low-molecular-weight heparin that is approved for both preoperative and postoperative initiation of prophylaxis; (2) the use of mandatory bilateral contrast venography, performed between days 6 and 15 postoperatively; (3) thromboprophylaxis continued until venography; (4) independent reading of venograms; and (5) assessment of clinically overt major bleeding by predefined criteria. Articles were excluded if no separate data could be obtained for patients undergoing elective hip surgery (in case of patient mix), or if they were reported more than once.
RESULTS: In the 1926 patients who used a preoperative regimen, the incidence of postoperative deep vein thrombosis was 19.2% (95% confidence interval [CI], 17%-21%). In the cohort of 925 patients who received a perioperative regimen, the rate of deep vein thrombosis was 12.4% (95% CI, 10%-14%), whereas in the group of 694 patients who received a postoperative regimen, it was 14.4% (95% CI, 12%-17%). The rate of major bleeding was 1.4% (95% CI, 1%-2%) in the preoperative group, 6.3% (95% CI, 5%-7%) in the perioperative group, and 2.5% (95% CI, 1%-3%) in the postoperative group.
CONCLUSIONS: We find no convincing evidence that starting prophylaxis preoperatively is associated with a lower incidence of venous thromboembolism than starting postoperatively. Perioperative regimens may lower the risk of postoperative thrombosis, but if so, this positive effect is offset by an increase in postoperative major bleeding.